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&lt;!-- Note: this line is an SGML comment --&gt;
&lt;!-- Note that all SGML markup is human-readable: no unprintables --&gt;

&lt;!DOCTYPE heuristic [ 
&lt;!ELEMENT heuristic    - - (purpose, inote?, realization, docinfo)&gt;
                              &lt;!-- The "top level" element for a --&gt;

                              &lt;!-- document structured according --&gt;
                              &lt;!-- to this DTD is: "heuristic".  --&gt;
                              &lt;!-- The "heuristic" element must  --&gt;
                              &lt;!-- contain exactly one "purpose" --&gt;
                              &lt;!-- element, optionally followed  --&gt;
                              &lt;!-- by an "inote", obligatorily   --&gt;

                              &lt;!-- followed by one "realization" --&gt;
                              &lt;!-- element, followed by one      --&gt;
                              &lt;!-- "docinfo" element, and        --&gt;
                              &lt;!-- nothing else!                 --&gt; 
&lt;!ATTLIST heuristic 
            version  CDATA  #FIXED "1.52" 
            security (unrestricted | internal.use | confidential |
                               need.to.know) #REQUIRED &gt;

&lt;!ELEMENT purpose      - - (#PCDATA) &gt;  
                              &lt;!-- "#PCDATA" means: parsable     --&gt;

                              &lt;!-- character data, i.e., text    --&gt;
                              &lt;!-- in which the "&lt;" character    --&gt;
                              &lt;!-- is treated as a start-of-     --&gt;
                              &lt;!-- tag character, etc.           --&gt;
                                        
&lt;!ELEMENT inote        - - (#PCDATA) &gt;
&lt;!ELEMENT realization  - - (point+) &gt;   &lt;!-- a "realization"     --&gt;

                              &lt;!-- consists of 1 or more "points"--&gt;

&lt;!ELEMENT point        - - (title, text+) &gt;  &lt;!-- a "point"      --&gt;
                              &lt;!-- must contain one "title",     --&gt;
                              &lt;!-- followed by 1 or more "text"  --&gt;
                              &lt;!-- elements                      --&gt;

  &lt;!ELEMENT title      - - (#PCDATA) &gt;    &lt;!-- a "title" element --&gt;
                              &lt;!-- can contain only characters,  --&gt;
                              &lt;!-- with no further embedded      --&gt;
                              &lt;!-- elements                      --&gt;

  &lt;!ELEMENT text       - - (#PCDATA) +(quote | institution | ruler | 
                               list | product | link | country) &gt;

                              &lt;!-- a text element can contain    --&gt;
                              &lt;!-- zero or any number of quote,  --&gt;
                              &lt;!-- institution, ruler, list...   --&gt;
                              &lt;!-- elements, as well as          --&gt;
                              &lt;!-- character text....            --&gt;

&lt;!ELEMENT docinfo      - - (url, author, auth.eaddr, rev.date) &gt;

&lt;!ELEMENT url          - - (server, account, page.id) &gt;
  &lt;!ELEMENT server     - - (#PCDATA) &gt;
  &lt;!ELEMENT account    - - (#PCDATA) &gt;
  &lt;!ELEMENT page.id    - - (#PCDATA) &gt;
&lt;!ELEMENT author       - - (given.name,sur.name,credential*) &gt;
  &lt;!ELEMENT given.name - - (#PCDATA) &gt;
  &lt;!ELEMENT sur.name   - - (#PCDATA) &gt;

  &lt;!ELEMENT credential - - (#PCDATA) &gt;
&lt;!ELEMENT auth.eaddr   - - (#PCDATA) &gt;
&lt;!ELEMENT rev.date     - - (rev.yr, rev.mo, rev.da) &gt;
  &lt;!ELEMENT rev.yr     - - (#PCDATA) &gt;
  &lt;!ELEMENT rev.mo     - - (#PCDATA) &gt;
  &lt;!ELEMENT rev.da     - - (#PCDATA) &gt;

&lt;!ELEMENT quote        - - (#PCDATA) +(quote | institution | 
                               product | ruler | country) &gt;
&lt;!ATTLIST quote 
            type     (copied.text | hearsay | memory | ipse.dixit | 
                               idiom | fictive | text.as.object | 
                               other) #REQUIRED
            source   CDATA  #IMPLIED &gt;

&lt;!ELEMENT link         - - (#PCDATA) &gt;
&lt;!ATTLIST link
            tgt      CDATA  #REQUIRED &gt; 
 
&lt;!ELEMENT institution  - - (#PCDATA) &gt;
&lt;!ATTLIST institution
            type     (corp | school | other) #REQUIRED &gt;
&lt;!ELEMENT product      - - (#PCDATA) &gt;

&lt;!ELEMENT ruler        - - (#PCDATA) &gt;
&lt;!ATTLIST ruler
            type     (king | prince | queen | president | 
                               prime.minister | other) #REQUIRED &gt;
&lt;!ELEMENT country      - - (#PCDATA) &gt;
&lt;!ELEMENT list         - - (item+) &gt;
  &lt;!ELEMENT item       - - (#PCDATA) +(quote | institution | 
                               product | ruler | list) &gt;

&lt;!ELEMENT i            - - (#PCDATA) &gt;
 
&lt;!ENTITY % THINK  "include" &gt;

&lt;!ENTITY % TAGS   "ignore" &gt;
&lt;!ENTITY % NOTAGS "include" &gt;
&lt;!ENTITY   lt     "&amp;#060;" &gt;

&lt;?STYLESPEC "Style1" "heuristic.ssh" &gt;
]&gt;
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